In the Democratic primaries last winter, Sen. John Edwards came on with the effervescence of uncorked champagne: An easygoing, relentlessly cheerful man, who barely six years into his political career has fashioned a reputation as one of his generation's most skilled public performers.

Beneath the simple appeal of his performances, however, is a life story of uncommon complexity. Far from easygoing, Edwards has shown a drive and discipline that are notable even by the standards of his former career, as a trial lawyer, and his current one, as a first-term senator from North Carolina who now has a spot on the Democratic presidential ticket.

Edwards's sunny-side-up approach to campaigning -- which made a winning impression with voters but yielded only two actual wins in the nominating contest -- is entirely authentic, according to many people who have worked for and with him. But this cheerful exterior also obscures an ambition that was fueled in youth by resentment at the snobbery he saw aimed against his working-class father, and in middle age by the grief that flowed from the death of a beloved teenage son.

Sen. John F. Kerry's decision yesterday to summon Edwards, 51, as his running mate on the Democratic ticket this fall ensures that this arresting -- and in some places controversial -- biography will become well-known to Americans over the next four months. It also sets up one of the most vivid stylistic and substantive contrasts imaginable.

Edwards, whose Senate years have won him praise for being energetic and a quick study but produced modest legislative achievements, had just graduated from North Carolina State University when Richard B. Cheney first held a senior White House position, in 1974. With a smooth-spoken style and a mop of golden hair, Edwards represents an entirely different breed of politician than the gruff and bald vice president. The Democrat became a wealthy man by suing corporations. The Republican became a wealthy man by being chief executive of a major energy services corporation, and as vice president he represents an administration that disdains trial lawyers and has sought legislation to curb their influence.

Cheney did not bring conventional political assets to the campaign in 2000, but with a quarter-century of Washington experience in Congress and the executive branch, his value to President Bush was obvious once it came time to govern. With Edwards, the situation is reversed. He brings a dynamism and theatrical presence that many Democrats say Kerry lacks, but his governing credentials are far less substantial.

In the Senate, Edwards had signature issues. The most prominent was his effort, in which he joined forces with Republican Sen. John McCain (Ariz.), to craft "patients' rights" legislation allowing people to sue HMOs. The Senate forged a compromise among its members to pass a bill but never could reach agreement with the House over a competing version. He also had signature strengths, including an ability to rapidly distill complex issues and describe them in compelling human terms.

Mostly, though, Edwards has been known in Washington for an ability to impress audiences, and he put himself at the front of the political pack with extraordinary speed. This was exactly the trait that he first displayed in North Carolina.

When Edwards first decided to run for the Senate against Republican incumbent Lauch Faircloth in 1998, even his own mother did not quite grasp the reach of her son's ambition. As she recalled it last year to the News & Observer in Raleigh, N.C., Bobbie Edwards said, "That's great. So you are going to run for the state Senate."

"Oh, no, Mama," the candidate replied. "The U.S. Senate."

"He skipped all the lower rungs," said Ferrel Guillory, an analyst of southern politics at the University of North Carolina at Chapel Hill. In the primary, Edwards edged out a Democrat who initially had more backing from the party establishment, then went on to beat Faircloth by 4 percentage points. He did it by spending about $6 million of his own money and by striking the populist themes that were his mark earlier as a trial lawyer and later as a presidential candidate. "What we learned in 1998 was his ability to blend his personal skills and his biography and convert that into a policy message," Guillory said.

One of the most important parts of Edwards's biography is one he rarely speaks of publicly. It is the 1996 car accident that killed his 16-year-old son, Wade. Edwards and his wife, Elizabeth, whom he met at the University of North Carolina law school and married in 1977, refashioned their lives after this tragedy.

On the personal side, they decided to seek fertility treatments -- Elizabeth Edwards was then in her late forties -- to have two more children in addition to their daughter, Cate, who was then in high school. On the career side, Edwards decided soon after to plunge into politics. He displayed interest before, but it was episodic -- he did not vote in some elections in the late 1980s and early 1990s. Soon he was running for the U.S. Senate. Some friends say that the family tragedy was in some sense liberating -- an electoral defeat could hardly add to the sense of loss he already felt, while a victory could lend ennobling purpose to an otherwise incomprehensible loss.

"The one thing a child's death does is wipe the slate clean for you," Elizabeth Edwards told the Raleigh newspaper.